Nonequilibrium characteristics in all-superconducting tunnel structures

TL;DR

This paper investigates the nonequilibrium behavior of superconducting tunnel structures with a small superconducting island, revealing distinct heating effects and hysteresis phenomena depending on the electron relaxation regime.

Contribution

It introduces a comprehensive analysis of both far-from-equilibrium and quasiequilibrium regimes, including the crossover, using a derived collision integral for superconductors.

Findings

Supercurrent suppression at low voltages indicates anomalous heating.

Hysteresis near the gap edge $2\\Delta/e$ reflects nonequilibrium distribution effects.

Distinct signatures differentiate far-from-equilibrium and quasiequilibrium states.

Abstract

We study the nonequilibrium characteristics of superconducting tunnel structures in the case when one of the superconductors is a small island confined between large superconductors. The state of this island can be probed for example via the supercurrent flowing through it. We study both the far-from-equilibrium limit when the rate of injection for the electrons into the island exceeds the energy relaxation inside it, and the quasiequilibrium limit when the electrons equilibrate between themselves. We also address the crossover between these limits employing the collision integral derived for the superconducting case. The clearest signatures of the nonequilibrium limit are the anomalous heating effects seen as a supercurrent suppression at low voltages, and the hysteresis at voltages close to the gap edge $2\Delta/e$, resulting from the peculiar form of the nonequilibrium distribution function.